The present invention relates to a magneto-optical recording medium, such as a magneto-optical disk, a magneto-optical tape, and a magneto-optical card, for use with a magneto-optical recording and reproducing apparatus.
A magneto-optical recording medium has been put in practical use as an erasable optical recording medium. However, such a magneto-optical recording medium has a drawback that reproducing characteristics are deteriorated as the diameter of a recording bit serving as a recording magnetic domain and an interval between the recording bits become smaller than a beam spot of a light beam emitted from a semiconductor laser.
The above drawback is caused by an event that individual recording bits can no longer be reproduced separately because the beam spot of a light beam focused on a target recording bit also encompasses recording bits adjacent to the same.
In order to eliminate the above drawback, Japanese Laid-open Patent Application No. 150418/1994 (Japanese Official Gazette Tokukaihei No. 6-150418, published on May 31, 1994) proposes a magneto-optical recording medium having (1) a reproducing layer whose magnetization direction is in-plane at room temperature and shifts to perpendicular with increasing temperatures; (2) a recording layer which is magneto-statically coupled to the reproducing layer; and (3) a non-magnetic intermediate layer provided between the reproducing layer and recording layer.
According to the above arrangement, the recording bits within a portion having the in-plane magnetization can be masked. Thus, even if the beam spot of a focused light beam encompasses more than one recording bit, the individual recording bits can be reproduced separately.
Also, Japanese Laid-open Patent Application No. 7350/1996 (Japanese Official Gazette Tokukaihei No. 8-7350, published on Jan. 12, 1996) and Japanese Laid-open Patent Application No. 21595/1998 (Japanese Official Gazette Tokukaihei No. 10-21595, published on Jan. 23, 1998) show a reproducing method, in which a magnetic domain in the recording layer is transferred to the reproducing layer while the magnetic domain is being expanded by applying an external reproducing magnetic field.
However, the method disclosed in Japanese Laid-open Patent Application No. 150418/1994 supra reveals that, when information is recorded and reproduced from the recording bits having smaller diameter and interval, a reproducing signal becomes less intensified, thereby making it impossible to obtain a satisfactory reproducing signal.
Also, the method disclosed in Japanese Laid-open Patent Application No. 7350/1996 supra has a problem that, when the recording density is increased and so is the number of bits under the reproducing magnetic domain, the reproducing layer receives the magnetic fields from more than one recording bit in the recording layer. In this case, the reproducing layer can not receive the magnetic field from the target reproducing bit alone.
Japanese Laid-open Patent Application No. 21595/1998 supra shows the magnetic domain expanding method with magneto-static coupling. According to this method, a second magnetic layer has a function of selecting a magnetic domain in the recording layer, and the magnetization thereof has temperature characteristics that the direction thereof shifts from in-plane to perpendicular with increasing temperatures. In this case, magnetization has to be transferred in two steps. To be more specific, the magnetization of the recording layer is transferred to the second magnetic layer by means of exchanged coupling first, and thence to the reproducing layer by means of magneto-static coupling. In other words, accurate information transfer from the recording layer to the reproducing layer involves a complicated procedure.
The present invention is devised to solve the above problems, and therefore, has an object to provide a magneto-optical recording medium which can select a single recording magnetic domain in the recording layer accurately, and expand and transfer the same to the reproducing layer.
In order to fulfill the above and other objects, a magneto-optical recording medium of the present invention is furnished with:
a reproducing layer whose magnetization direction is in-plane at room temperature and shifts to perpendicular at or above a predetermined temperature Ttrans.;
a recording layer whose magnetization direction is perpendicular in a range between room temperature and a Curie temperature thereof, during which the recording layer being magneto-statically coupled to the reproducing layer;
a magnetic mask layer which is provided between the reproducing layer and recording layer with an intermediate layer on the reproducing layer side, and whose magnetization direction is in-plane at room temperature,
the magnetic mask layer being made of alloy including at least one kind of light rare earth metals and at least one kind of 3d transition metals.
According to the above arrangement, because the magnetic mask layer containing the light rare earth metal(s) and the 3d transition metal(s) is used, the magnetization of the recording layer can be masked in a stable manner, thereby improving a CNR as an effect.
Also, in order to fulfill the above and other objects, a magneto-optical recording medium is furnished with:
a reproducing layer whose magnetization direction is in-plane at room temperature and shifts to perpendicular at or above a predetermined temperature Ttrans.;
a recording layer whose magnetization direction is perpendicular in a range between room temperature and a Curie temperature thereof, during which the recording layer being magneto-statically coupled to the reproducing layer;
a magnetic mask layer between the reproducing layer and recording layer with an intermediate layer on the reproducing layer side, whose magnetization direction is in-plane at room temperature,
magnetization of the magnetic mask layer being larger than magnetization of the recording layer at least in a range between room temperature and the predetermined temperature Ttrans., and smaller at or above a predetermined temperature exceeding the predetermined temperature Ttrans.
According to the above arrangement, because the magnetic mask layer having larger magnetization than the recording layer up to the predetermined temperature Ttrans.is used, the magnetization of the recording layer can be masked in a stable manner, thereby improving a CNR as an effect.